1. Field of the Invention
This invention relates to a magnet roll for use in a developing machine using an electrophotographic technique such as a copying machine, a facsimile, a laser beam printer (LBP) or the like and a cleaning machine, and a method for producing the same.
2. Description of the Related Art
A magnet roll has been broadly utilized in a developing machine using an electrophotographic system such as a copying machine, a facsimile or the like. The magnet roll has a function of picking up developing agent from a developing agent box and delivering the pick-up developing agent to a photoreceptor. FIGS. 1 and 2 schematically show the construction of an embodiment of the magnet roll as described above. As shown in FIGS. 1 and 2, a metal sleeve 2 is rotatably provided around a magnet roll 1 to form a developing cylinder 3, and the developing cylinder 3 is disposed so as to confront a photosensitive drum 4. The delivering operation of the developing agent by the magnet roll 1 is performed with the assistance of plural magnetic poles which are magnetized on the surface of the magnet roll, and the intensity of magnetic force (surface magnetic flux density) and magnetic pattern of each magnetic pole is beforehand set in accordance with the role to be performed by the magnetic pole.
The following examples of magnet rolls have been known as a conventional magnet roll 1. One example is a magnet roll as shown in FIG. 3(I) comprising a cylindrical magnet body 5 which is formed by conducting an extrusion molding on resin bonded magnetic material, and a metal shaft 6 inserted into a hollow center of the cylindrical magnet body 5 over its whole longitudinal body. Another example is a magnet roll as shown in FIG. 3(II) comprising a single body having both end shaft portions 7 which are integrally formed using no metal shaft by conducting an injection molding on resin bonded magnet material. A third example is a magnet roll as shown in FIG. 3(III) comprising a solid cylindrical magnet body 9 and short shaft rods 8 inserted into both end portions of the magnet body 9.
The magnet rolls as described above have been generally produced through the following processes, that is, I) a molding process, II) a shaft-inserting process, III) a sizing process, IV) a process for demagnetizing magnets (hereinafter referred to as "demagnetizing process"), and V) a process for re-magnetizing magnets (hereinafter referred to as "re-magnetizing process").
The details of works of the respective processes are as follows.